Damage of Houses and Residential Areas by Niigata Prefecture Earthquakes (Part2)

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1 Proceedings of the Eighteenth () Interntionl Offshore nd Polr Engineering Conference Vncouver, BC, Cnd, July -11, Copyright by The Interntionl Society of Offshore nd Polr Engineers (ISOPE) ISBN (Set); ISBN (Set) Dmge of Houses nd Residentil Ares by Niigt Prefecture Erthqukes (Prt) Toru Tkt Soil Design Inc. Tokyo, Jpn Mmoru Fujii Toki University Kngw, Jpn Ktsuy Mtsushit Mi Homes Institute of Reserch nd Development Co., Ltd. Tokyo, Jpn Hirku Seki Knw University Ishikw, Jpn ABSTRACT The erthqukes of Chuetsu () nd Chuetsu offshore (7) in Niigt Prefecture, cused liquefction t mny loctions, nd lso cused dmges on the residences nd the residentil res due to the filure of ground. In the future, the judgment of liquefction on housing site will become importnt nd it will be thought tht the upgrde of soil investigtion nd liquefction countermesure is necessry. In Jpn, Swedish weight sounding (SWS) hs been widely used in soil investigtion on residentil res. Bsed on the result of SWS, the bering cpcity of ground cn be obtined. However, the judgment of liquefction is not obtined. This pper reports results of SWS, boring investigtion, stndrd penetrtion test (), nd three component cone penetrtion test () on the housing site which cught the liquefction dmge by the erthquke of Chuetsu offshore (7) in Niigt Prefecture. In ddition, it reports the pplicbility of the on the housing site of Jpn. KEY WORDS: Soil investigtion; cone penetrtion test; Swedish weight sounding; liquefction; residentil res. INTRODUCTION The Building Stndrd Lw of Jpn sys tht "It is necessry for the ground with the fer of the liquefction by n erthquke to confirm tht the hrmful dmge, trnsformtion, subsidence to the prt of building do not produce". It cn be sid tht the exmintion of the liquefction is essentil becuse this lw is pplied to the privte housing without exceptions. The problem of the liquefction on the housing sites in Jpn is viewed esily from documentry serch such s "mps for liquefction sites", becuse the SWS re common. In ddition, it is difficult to tke liquefction countermesure by privte housing finncilly, nd this is fctor to tke liquefction judgment esy. The simple judgment method of liquefction bsed on soil investigtion hs judgment method bsed on the (N-vlue) nd the (q c ). In Jpn, judgment method bsed on the is common. It is big fctor tht Jpnese design system bsed on N-vlue is estblished. However, it is rre tht the is performed for the soil investigtion on housing res becuse the is expensive. On the other hnd, the is not common in Jpn. This cuse is in the Jpnese ground where there is grvel crried by the fst flowing strem river from the hilly district to the estury. Therefore, soil investigtion using the is difficult in Jpn. However, the is economicl in comprison with the nd lbortory soil test. In ddition, the gives us soil clssifiction, bering cpcity, consolidtion of the ground, nd the position of groundwter level without the smpling of soil. In this respect, the is effective in the soil investigtion on housing sites. Most of this investigtion is used by the SWS first. Therefore, it is thought tht the trouble tht cone cnnot be penetrted get fewer becuse it cn estimte the penetrted power of cone bsed on the result of the SWS. This pper reports result of the SWS, boring investigtion, grin sie nlysis, the, the on the housing site tht hd been cught the liquefction dmge by the erthquke of Chuetsu offshore (7) in Niigt Prefecture. In ddition, it reports the current sttus of the seismic performnce evlution nd the pplicbility of the to the residentil res of Jpn. PLAN FOR GROUND INVESTIGATION The investigtion plce is two housing sites (Kshiwki- Mtsunmi nd Kshiwki-Hshib) tht cught the liquefction dmge by the erthquke of Chuetsu offshore (7) in Niigt Prefecture (Fig. 1). The mgnitude (M) of this erthquke ws.; the pek horiontl ccelertion t the ground surfce ( mx ) generted by this erthquke ws bout gl. The snd boil due to liquefction ws remrkbly generted on the both housing sites, nd differentil settlement ws cused in the houses. We investigted the three soundings of the SWS, the, nd the in this both sites. Moreover, the grin sie distribution ws nlyed nd the soil clssifiction ws exmined using the soil smples obtined from boring holes. 79

Tble 1. We used the -cone tht cn mesure skin friction (f s ) in ddition to generl corn tht mesured cone resistnce (q c ) nd pore wter pressure (u).

Mtsunmi Hshib These ground investigtion hs performed fter one month or more psses this erthquke though it is necessry to exmine idelly bsed on the result of ground investigtion before the erthquke.

se RESULTS OF THE GROUND INVESTIGATION Figure () shows ech investigtion results (boring log, the, the, the SWS) of Mtsunmi re, nd Fig. (b) shows one of Hshib re.

1m t Hshib re. The vlue of ech penetrtion resistnce distribution of the (N-vlue), the (q c ), the SWS (W, N ) shows similr tendency. We obtin mesurements t 1.m intervls from the, nd mesurements t.

Eqution 1 which evlutes N-vlue from the SWS results is proposed by Ind (19). N = 3.W.W +.5N +.

2 Tble 1. We used the -cone tht cn mesure skin friction (f s ) in ddition to generl corn tht mesured cone resistnce (q c ) nd pore wter pressure (u). Moreover, we mesured the position of groundwter level by the excess pore wter pressure dissiption test of the. Mtsunmi Hshib These ground investigtion hs performed fter one month or more psses this erthquke though it is necessry to exmine idelly bsed on the result of ground investigtion before the erthquke. The SWS hs been done in both residentil res before this erthquke. Therefore, the SWS hve gone gin to understnd the ground chrcteristic of the erthquke before nd fter. se RESULTS OF THE GROUND INVESTIGATION Figure () shows ech investigtion results (boring log, the, the, the SWS) of Mtsunmi re, nd Fig. (b) shows one of Hshib re. Mtsunmi re hd fine snd of N-vlue bout - in GL m. Hshib hd filling snd of N- vlue bout 5 in GL m on the old river. The position of groundwter level ws GL-3.3m t Mtsunmi re, nd GL-3.1m t Hshib re. The vlue of ech penetrtion resistnce distribution of the (N-vlue), the (q c ), the SWS (W, N ) shows similr tendency. We obtin mesurements t 1.m intervls from the, nd mesurements t.5m intervls from the SWS. On the other hnd, the hs n dvntge tht thin strtum cn be detected becuse we obtin continuous mesurements t.1m intervls from the. Eqution 1 which evlutes N-vlue from the SWS results is proposed by Ind (19). N = 3.W.W +.5N +.7 N ( cohesive ( sndy soil ) soil ) (1) Eqution which evlutes N-vlue from the results is proposed by Semtsu nd Suuki (5). Mtsunmi Fig. 1. Loction of investigtion site Tble 1. This ground investigtion nd the investigtion stndrd Exmintion item Swedish weight sounding (SWS) Cone penetrtion test () Stndrd penetrtion test () Stndrd No. JIS A11 JGS JIS A119-1 JIS A: Exmintion Vlue Sttic penetrtion resistnce (W, N ) Cone resistnce (q c ) Pore wter pressure (u) N-vlue Hshib Mximum grin sie Grin sie distribution curve Grin sie nlysis Fine frction content Note: JIS; Jpnese Industril Stndrd JGS; Jpnese Geotechnicl Society These investigtion methods were bsed on the ech stndrd shown in N =.3I 1.9 c In ddition, the conversion method of soil clssifiction using the vlue of q c, f s, nd u is proposed. Robertson et l. (199) proposes soil behvior type index (I c ) clculted from the following eqution: I where Q t is normlied cone resistnce ((q t - σ vo )/σ vo ), nd F r is normlied friction rtio (f s /(q t - σ vo )). The vlue of I c gives us soil clssifiction shown in Tble. Moreover, Eqution which evlutes fine frction content (F c ) from the vlue of I c is proposed by Semtsu nd Suuki (5). Tble. Soil clssifiction using I c ( ) ( I ) c q. ( q.mp) t t > ( q.mp) ( 3.7 log Q ) + ( log F + 1. ) C = t r. F C = I C Division No. I c Soil clssifiction 1 <1.31 grvelly snd 1.31~.5 snd to silty snd 3.5~. silty snd to sndy silt.~.95 silt to silty cly 5.95~3. silty cly to cly 3.< orgnic mteril t () (3) () 75

3 (m) Grin Sie Distribution (%) 5 3 Silt or Grvel N-vlue qc (MP) fs (MP) u (MP).1.. W.5 (kn) 1 N 3.75 Grvelly snd Silty Boring Log dt dt SWS dt Fig. (). The result of the ground investigtion () (m) Silty Grin Sie Distribution 5 3 Silt or Grvel N-vlue qc (MP) fs (MP) u (MP) W N.1.. Boring (kn) Grvel Silty Silty Boring Log dt dt SWS dt Fig. (b). The result of the ground investigtion (Site: Hshib re) 751

4 The results of the comprison between I c nd boring log re shown in Fig. 3, nd the comprison between fine frction content bsed on the results nd grin sie nlysis re shown in Figure, nd the comprison between N-vlue by the, the SWS nd the re shown in Fig. 5. The soil clssifiction nd F c using the results ws comprtively similr to the results of boring log nd grin sie nlysis. However, there is difference in detiled prt of both soil clssifiction, nd there is n enough correltion in rough division such s grvel, sndy, silt, nd cly. Moreover, the results of N-vlue by the, the SWS gree with it by the. Figure shows the comprison of the SWS results before the erthquke nd fter it t Mtsunmi re. The SWS results t Hshib (m) Grvelly snd Soil clssifiction by the Silty Soil behvior type index (Ic) 1 3 re cn't be comprble, becuse the investigtion depth (GL-.5 ~ -.5m) is too shllow becuse of the hrd embnkment. In the result t Mtsunmi re, N-vlue evluted using the SWS fter the erthquke re smller thn ones before the erthquke. Generlly, it is sid tht the ground, which liquefied in the pst, increses the liquefction resistnce, becuse the wet density increses. This result implies tht there is not the effect of compction due to the erthquke motion. This result is only t one re nd it cnnot be sid enough volume of dt. However, there is cse with little compction effect of erthquke like this result. We think tht the ground tht is not equl in density, the time of the erthquke motion nd the residul displcement fter the erthquke re relted to the fctor of this result. Therefore, we think tht the ground tht hs been cused liquefction due to the erthquke is possibility of liquefction due to similr erthquke gin. Fine frction content (F C ) (%) Fine frction content (F C ) (%) Grin sie nlysis Silty Boring Log 1 1 Grin sie nlysis 1 1 (m) Silty Grvel Soil clssifiction by the Grvel snd Slty cly to Soil behvior type index (Ic) 1 3 Fig.. Comprisons between fine frction content bsed on the results nd grin sie nlysis N -vlue 3 SWS N -vlue 3 SWS Boring Log Silty Silty Fig. 3. Comprisons between soil clssifiction bsed on the results nd boring log (reference tble.) Fig. 5. Comprisons between N-vlue by the, the SWS nd the 75

5 N- vlue 3 5 before erthquke fter erthquke Ave(before erthquke) Ave(fter erthquke) F L -vlue 1 F L -vlue 1 Fig.. Comprisons of the SWS results before the erthquke nd fter one t Mtsunmi re 1 1 COMPARISON BETWEEN THE JUDGEMENT METHOD OF LIQUEFACTION USING AND 1 1 The method of judging liquefction is the detiled one nd the simple one, nd this reserch used the simple method. The outline is shown s follows: () Detiled judgment method The liquefction resistnce rtio (R) is mesured from the results of cyclic trixil test using the undisturbed smple obtined in situ, nd the cyclic sher stress rtio (L) is obtined from seismic response nlysis etc. Thus, we obtin the liquefction sfety rte (F L (: R/L)). (b) Simple judgment method The liquefction resistnce rtio (R) is converted from the results of ground investigtion or lbortory test, nd the sher stress rtio (L) is clculted from the design erthquke motion. Thus, we obtin the liquefction sfety rte (F L (: R/L)). The liquefction resistnce rtio (R) in ny depth cn be converted from some methods. Recommendtions for design n of building foundtions issued by Architecturl Institute of Jpn (1) shows the following two methods s method with high relibility. 1) Method of presuming R bsed on the results (N-vlue) nd the grin sie nlysis results (F C ). ) Method of presuming R bsed on the results (q c, f s nd u). The cyclic sher stress rtio (L) is clculted from the following eqution: τ d mx σ L = = rn rd (5) σ ' g σ ' whereτ d (stress reduction coefficient); σ nd σ' (totl nd effective verticl overburden stresses); g (ccelertion of grvity); mx ( pek horiontl ccelertion t the ground surfce generted by the erthquke): r n (correction coefficient to cyclic count(=.1(m-1); M = mgnitude)): r d (decrese coefficient (= ; = depth (meter))). Figure 7 shows the depth distribution of F L on input erthquke condition (M:., mx : 5gl) used to design generlly. Figure shows the depth distribution of F L by vlue on the erthquke of Chuetsu offshore (7) in Niigt Prefecture (M:., mx : gl). The depth distribution of F L bsed on the results nd bsed on the Fig. 7. The depth distribution of F L on input erthquke condition (M:., mx :5gl) used to design generlly 1 1 F L -vlue 1 Fig.. The depth distribution of F L by vlue on the erthquke of Chuetsu offshore (7) in Niigt Prefecture (M:., mx :gl) nd the grin sie nlysis results re roughly corresponding though F L bsed on the results is little smller thn it bsed on the nd the grin sie nlysis results. There is little liquefied lyer (F L <1.) t the design condition on both res (Fig. 7). On the other hnd, when the erthquke condition mesured in this time is given, the liquefied lyer on Hshib re is clculted GL-3~-7m, nd it on Mtsunmi re is clculted GL-3~-m(Fig. ). The snd boil is gretly generted due to the liquefction on this erthquke in both housing res. It cn be sid tht F L shown in Figure 7 lmost grees with this phenomenon. 1 1 F L -vlue 1 753

6 EVALUATION OF THE LIQUEFACTION INFLUENCE IN THE HOUSING The dmge of the housing cused by liquefction becomes t the position of the liquefction lyer tht is thick nd shllow remrkble. The dmge of the foundtion nd the housing is different in the level, the thickness, the depth of the liquefction lyer etc. Moreover, it is not relted to the dmge of the housing nd the residentil re immeditely even if the liquefction lyer is in the ground. Therefore, it is necessry to evlute the influence tht liquefction gives the housing. In this reserch, the three evlution methods of the influence (, b, c) tht liquefction gives the housing in the flt ground re used. The methods re shown s follows. () Evlution method by the liquefction index (P L ) (N.L.A., 199) The liquefction index (P L ) is proposed s one index tht evluted the influence tht liquefction gives the housing. It is clculted from the following eqution: P L = (1 F ) (.5) d Tble 3 shows the liquefction judgment division by P L ccording to the liquefction region-oning mnul (199). Tble 3. The liquefction judgment division by P L Liquefction extent of the impct Middle ground motion ( 1- F ) L L P L -vlue Lrge ground motion Smll P L 5 P L 5 Lrge 5<P L 15 5<P L Huge 15<P L <P L (b) Evlution method by the dynmic surfce displcement (D cy ) (A.I.J., 1). The dynmic surfce displcement (D cy ) is proposed s one index tht shows the reltion between the dynmic horiontl displcement of the ground surfce cused by liquefction nd the dmge level of the housing. It depends on the following procedures when the result is used. 1) N-vlue converted by the results (Eq. ) is treted s N-vlue by the results. ) Corrected N-vlue (N ) to F c nd σ' is clculted from Eqution 7. N = N 1 + N f where N 1 = corrected N-vlue concerning confining pressure ' ( N1 = 9 σ N ): N f = corrected increment vlue concerning F c shown in Figure 9. 3) Cyclic sher stress of the both depth corresponding to N nd τ d /σ' (γ cy ) is presumed from Figure. ) It is ssumed tht γ cy of the ech depth is generted in the sme direction. And, γ cy is integrted into verticl direction. And, the mximum horiontl displcement by integrting γ cy into verticl direction is obtined. 5) The mximum horiontl displcement is treted s the dynmic surfce displcement (D cy ). And the influence tht liquefction gives the housing is evluted to the vlue of D cy shown in Tble. () (7) (c) Evlution method using the reltion of two-lyer ground (the liquefied lyer nd the non-liquefied lyer( U.D.Co., 3) Collected N-vlue increse ( Nf ) Fig. 9. Reltion between F c nd ΔN f τd/σ' Fine frction content (F c (%)) γcy=% γcy=% γcy=% γcy=1% γcy=.5% 3 Collected N -vlue (N ) Fig.. Reltion between N, γ cy nd τ d /σ Tble. Reltion between D cy nd the dmge level of liquefction D cy (cm) Liquefction extent of the impct None 5 Minor 5- Smll - Medium - Lrge Huge Liquefction lyer thickness ( H (m)) A liquefction Middle ground motion A liquefction Lrge ground motion Nom-liquefction lyer thickness (H 1 (m)) Fig. 11. The borderline of liquefction in reltion between H 1 nd H The cly soil or unsturted soils tht is shllower thn the position of groundwter level re the soil lyers where the possibility of liquefction is little. Therefore, even if the sturtion sndy soil under groundwter level is cused by liquefction t the erthquke, it might 75

7 not influence the housing re nd the housing by non-liquefied lyer on the surfce ground. Figure 11 shows borderline of liquefction in the both erthquke motion. This plotted points in Figure 11 gives us the presence of dmge by liquefction. Tble 5. shows the evlution result of the influence tht liquefction gives the housing using method 1-3. It is clculted tht P L =. ~ 1. (Mtsunmi), P L =. ~ 1.1 (Hshib), D cy =. ~ 1. (Mtsunmi), nd D cy =.3 ~ 1.5 (Hshib), nd it cn be sid tht the influence by liquefction on the housing is little in the design erthquke condition ( mx = 5gl). However, it is clculted tht P L = 9. ~ 1.7 (Mtsunmi), P L = 1.9 ~ 1. (Hshib), D cy =. ~ 15.3 (Mtsunmi), nd D cy = 7. ~ 11.5 (Hshib), nd it cn be sid tht the influence by liquefction on the housing is very lrge in this seismic condition. In ddition, the evlution method using Tble 5. The evlution result of the influence tht liquefction gives the housing Method Site:Mtsunmi re Erthquke emotion Ground Investigtion dt M mx,f c P L -vlue 1. Judgment Smll Smll. 5 gl gl Erthquke emotion Method M mx Reference Tble. 3. D cy 1. b Judgment Minor None Tble.. H 1 (m) 5. - c H (m) 1.5 Fig.11 Judgment OK OK P L -vlue Judgment Lrge Lrge Tble.3. D cy b Judgment Middle Middle Tble.. H 1 (m) c H (m).5. Judgment NG NG Ground Investigtion dt,f c P L -vlue 1.1. Judgment Smll Smll D cy b gl Judgment Minor Minor H 1 (m) c H (m). 1. Judgment OK OK. P L -vlue Judgment Lrge Lrge D cy b Judgment Smll Middle gl H 1 (m).. c H (m) Judgment NG NG Note: NG; A-liquefction OK; Non-liquefction Fig. 11 Reference Tble. 3 Tble. Fig.11 Tble.3 Tble. Fig. 11 the reltion of the non-liquefied lyer nd the liquefied lyer of the ground surfce gives us the similr result to method 1nd method. Thus, we obtined n lmost similr result by three methods. Moreover, n obviously different results in cse of design condition nd this time erthquke condition is obtined. We thought tht the liquefied lyer becme remrkbly thick becuse this erthquke motion is lrger thn the erthquke motion using the designs. The lyer tht chnges into the liquefied lyer by the difference of this erthquke motion is thought to be snd lyer of N-vlue 15~. CONCLUSIONS This pper reports result of SWS, boring investigtion, stndrd penetrtion test (), nd three component cone penetrtion test () on the housing res tht hd been cught the liquefction dmge by the erthquke of Chuetsu offshore (7) in Niigt Prefecture. As result, the following conclusions were obtined. () The judgment method of liquefction by the results ws compred with the judgment method by the nd grin sie nlysis results. It hs been obtined result similr to both though it is simple method. In ddition, these judgment results were ble to explin the housing dmge nd the boil snd cused by n ctul liquefction. (b) It ws observed tht the mximum horiontl ccelertion ws lrger thn the designed ccelertion used in generl, nd the vlue of seismic intensity scle is strong with +. Therefore, it hs been understood tht the non-liquefied lyer in the design condition becme liquefied lyer becuse of this erthquke condition. It is necessry to estblish the soil investigtion of privte housing tht used by the judgment of liquefction in Jpn. It my be sid tht the is the investigtion method tht is influentil t the point where there is esily liquefction judgment. We think tht it will be necessry to suggest ground improvement method of housing sites imed for liquefction countermesure s well s investigtion method in future. REFERENCES Ind M. (19), Interprettion of Swedish weight sounding, Monthly Mgine of Jpnese Geotechnicl Society, Vol., No., pp Semtsu T nd Suuki Y(5), Correltion between dt nd soil chrcteristics,prt1:evlution of soil clssifiction nd N- vlue, Jpnese Geotechnicl Society. Robertson, P.K. (199), Soil clssifiction using the cone penetrtion test, Cndin Geotechnicl Journl, Vol. 7, No. 1, pp Architecturl Institute of Jpn (1), Recommendtions for design of building foundtions. Ntionl Lnd Agency (199), The liquefction region-oning mnul Urbn Development Corportion (3), A seismic design mnul on residentil re ( pln), pp

Vadose Zone Hydrology

Vadose Zone Hydrology Objectives Vdose Zone Hydrology 1. Review bsic concepts nd terminology of soil physics. 2. Understnd the role of wter-tble dynmics in GW-SW interction. Drcy s lw is useful in region A. Some knowledge of